The big rock alien was an inhabitant of Neutopia. In June 3011 (6ACV20), it encountered a group of Earthican people among which was the Planet Express crew and - confused by the concept of male and female, because the members of its species are solely neuchachos - both neutered them and altered their genders. The alien was disintegrated by Zapp as it was about to return the Earthicans their genders.

Big rock alien: Your genders differ in many ways. But as with all things that are different - chocolate and vanilla, Mac and PC - one is always clearly better.Bender: Chocolate, Mac, men. The end.Big rock alien: Well, I've got nothing to do for the next eight million years. Therefore, I will administer a series of tests to determine the superior gender.

Big rock alien: I find both genders supremely disappointing. The real reason I administered this bizarre, outer-space test was to teach you to work together! But you couldn't. Thanks to you, I lost my bet with the Borax Kid.Fry: Never bet against me being stupid.Big rock alien: Enough! Your gender differences have kept you from achieving harmony. There is only one way to resolve this conflict. [The big rock alien neuters the Earthicans.] I have freed you from the tyranny of gender. Now go in peace. Or actually stay here. I'll go in peace.

Big rock alien: I have decided, after little thought, to return your genders. [The big rock alien makes the men into women and the women into men. The Earthicans complain.] Okay. Stop yelling at me! It was an innocent mistake. Allow me to rectify it.[The big rock alien is shot by Zapp.]